1. Field of the Invention
The present invention relates to a fiber sheet having a resin sheet and an optical fiber wired on the resin sheet, and also to a manufacturing method for the fiber sheet.
2. Description of the Related Art
A fiber sheet having a resin sheet and an optical fiber preliminarily wired on the resin sheet so as to correspond to the connecting relation between optical components is used in an optical module, printed circuit board, or optical transmission device. There is a demand for the structure of a fiber sheet and its manufacturing method with no increase in optical loss even in the case of application of an external force. A conventional fiber sheet is formed by preparing a first resin sheet having an adhesive layer on one side, bonding an optical fiber through the adhesive layer to the first resin sheet by applying a pressure to thereby wire the optical fiber on the first resin sheet, and attaching a second resin sheet to the first resin sheet so that the optical fiber is sandwiched therebetween. Such a fiber sheet is frequently used in an optical module or the like, in which a plurality of optical fibers are preliminarily wired so as to correspond to the connecting relation between optical components.
In the conventional fiber sheet, there is a possibility of bending of the optical fibers by an external force applied during the manufacture or use of the fiber sheet at a cross point where the optical fibers cross each other, causing an increase in optical loss. In the case of applying the fiber sheet to an optical module or the like, the fiber sheet is required to support high-density mounting, so that it must have a resistance against an external force. Further, in the conventional fiber sheet, the optical fibers are wired on the first resin sheet in consideration of only the allowable bend radius of each optical fiber in the plane of the resin sheet.
Accordingly, in the case that the fiber sheet is bent with a radius of curvature smaller than the allowable bend radius of each optical fiber, the optical loss increases to cause a reduction in reliability. As a result, it is difficult to mount the fiber sheet in its bent condition, and in the case of using the fiber sheet for wiring between optical components in an optical module, the mounting area of the optical components becomes large. Further, in the case of using the fiber sheet for wiring between adjacent printed circuit boards, the distance between the adjacent printed circuit boards becomes large.